According to French newspaper Le Monde, the fire broke out in the attic of the historic monument before spreading to engulf a large section of the roof.
A spokesperson for the cathedral said the blaze was first reported at 5.50pm (GMT) and the building was evacuated soon after.
The cathedral is one the finest example of French Gothic architecture in Europe, and one of the most visited buildings in the world.
Notre Dame - which means 'Our Lady' - was build in 1160 and completed by 1260, and has been modified on a number of occasions throughout the century.
It is the cathedral of the Archdiocese of Paris, and is vistied by some 12million people every year.